Python String format() method

January 11, 2021 3 minutes read

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Python String format() method

The format() method in Python, formats the specified value(s) and inserts them inside the string’s replacement fields and returns the formatted string.

The replacement fields for the values is defined using curly braces {}.

Code

print("My name is {}. I love {}".format("Pylenin", "Python"))

Output

My name is Pylenin. I love Python

How does it work?

When placeholders {} in the string are empty, Python will replace the values passed through str.format() in order.

Check out the following example.

Code

# Method 1
print("My name is {}. I love {}".format("Pylenin", "Python"))
print("My name is {}. I love {}".format("Python", "Pylenin"))

Output

My name is Pylenin. I love Python
My name is Python. I love Pylenin

Formatters with Positional Arguments

Similar to indexing in strings, the values present inside string.format() method also start with index 0 and increments by 1 with every value. These index numbers can be passed into the curly braces(replacement fields) serving as the placeholders in the original string.

Let’s look at the following example.

Code

print("My name is {0}. I love {1}".format("Pylenin", "Python"))
print("My name is {1}. I love {0}".format("Pylenin", "Python"))

Output

My name is Pylenin. I love Python
My name is Python. I love Pylenin

Beware - If you try to escape the index 0 or start with a different number, Python will throw you an IndexError.

Code

print("My name is {1}. I love {2}".format("Pylenin", "Python"))

Output

Traceback (most recent call last):
  File "some_file_location", line 2, in <module>
    print("My name is {1}. I love {2}".format("Pylenin", "Python"))
IndexError: Replacement index 2 out of range for positional args tuple

It basically means, you are trying to access the 2nd index from the values within the string.format() method and it doesn’t exist.

However, the following example will work.

Code

print("My name is {1}. I love {2}".format("Pylenin", "Python", "Programming"))```

**Output**

```bash
My name is Python. I love Programming

In this case, you have values inside the string.format() method with index from 0 to 2. You are just not using the 0th index in your string.

Formatters with Keyword Arguments

Instead of empty curly braces or curly braces with index, you can also use keyword arguments.

Code

print("My name is {name}. I love {language}"\
      .format(name="Pylenin", language="Python"))

Output

My name is Pylenin. I love Python

Keyword arguments are like keys in a dictionary. Their order doesn’t matter, as they are matched against a name.

Specifying Formatting Type

You can also use a specific format in string formatting in Python.

Let’s look at the below example.

Code

# integer
print("Integer representation of 99 is {:d}".format(99))

# float
print("Float representation of 99 is {:.2f}".format(99))

# binary
print("Binary representation of 99 is {:b}".format(99))

# exponent
print("Exponential representation of 99 is {:.2e}".format(99))

Output

Integer representation of 99 is 99
Float representation of 99 is 99.00
Binary representation of 99 is 1100011
Exponential representation of 99 is 9.90e+01

You can find a list of available formatters here.

Python offers 3 other ways of String Formatting. Check out the definite guide to Python String Formatting

Python String format() method

How does it work?

Formatters with Positional Arguments

Formatters with Keyword Arguments

Specifying Formatting Type

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